Burner assembly and method for reducing nox emissions

ABSTRACT

A burner assembly for combusting fuel in a combustion zone to reduce NOx emissions includes a water spray subassembly including a water outlet configured to direct water at an angle with respect to an axis of the burner assembly, the water outlet further configured to direct the water in a direction for mixing with the air upstream of the combustion zone. A method is also provided for combusting fuel in a combustion zone to reduce NO x  emissions.

BACKGROUND

Gas burners are employed in a wide variety of commercial and industrialapplications. For example, gas burners may be used to vaporize cryogenicfluid such as liquefied natural gas. Specifically, cryogenic fluid canbe heated in a submerged combustion vaporizer (SCV). An SCV typicallyincludes heat exchanger tubing and a water tank in which the tubing issubmerged. The cryogenic fluid flows through the tubing. The SCV furtherincludes a gas burner that fires into a duct system. The duct system hasperforated sections, known as sparger tubes, that direct the burnerexhaust to bubble upward through the water in the tank. The exhaust thenheats the water and the submerged tubing so that the cryogenic fluidflowing through the tubing also becomes heated. Nitrogen oxides (NOx) inthe exhaust are carried upward from the tank through a flue anddischarged into the atmosphere with the exhaust.

Despite many improvements in gas burners over the years, there remains acontinued need for further improvements. For example, there remains aneed for burners that are improved in at least one of efficiency,performance, emissions control, and cost.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a perspective, cross-sectional view of an embodiment of aburner assembly according to the invention.

FIG. 1B is a detail of a portion of the burner assembly illustrated inFIG. 1A.

FIG. 2 is a partial cross-sectional elevation view of a main burnerincorporating a water supply and a spray nozzle that can be used in theburner assembly illustrated in FIG. 1A.

FIG. 3A is a top view of a portion of the main burner illustrated inFIG. 2.

FIG. 3B is an elevation view of the portion of the main burnerillustrated in FIG. 3A.

FIG. 4 is a cross-sectional elevation view of a distal end portion ofthe main burner illustrated in FIG. 2.

FIG. 5A is an elevation view of a portion of a water spray subassemblythat can be used in the burner assembly illustrated in FIG. 1.

FIG. 5B is a top view of the water spray subassembly illustrated in FIG.5A.

FIG. 6 is an enlarged cross-sectional elevation view of a distal endportion of the main burner illustrated in FIG. 2.

FIG. 7 is an enlarged cross-sectional elevation view of anotherembodiment of a main burner.

DETAILED DESCRIPTION OF THE INVENTION

Although the invention is illustrated and described herein withreference to specific embodiments, the invention is not intended to belimited to the details shown. Rather, various modifications may be madein the details within the scope and range of equivalents of the claimsand without departing from the invention.

Generally, the burner assembly in the illustrated examples is a watercooled burner that is mostly or completely free of refractory material.A fuel source, which is preferably a supply of natural gas; and anoxidant source, which is preferably an air blower, provide the burnerwith streams of those reactants.

The burner assembly preferably includes a water injection system. Thissystem includes a water line that communicates with a water source. Thewater source is preferably a tank of stored water, but could optionallybe the publicly available water supply.

The burner assembly is especially useful in combination with LNGsubmerged combustion vaporizers (SCVs). Such vaporizers are useful forheating and/or vaporization of cryogenic and low temperature fluids.Though frequently used with oxygen, nitrogen, ethylene, ammonia, andpropane, such vaporizer systems are optionally used for vaporization ofLNG, e.g., in base-load and peak-shaving regasification facilities.

The SCV is an indirect fired heat exchanger with the burner and aprocess tube coil that may be contained within a single vessel. Thedesign is based on the submerged exhaust principle whereby the burnercombustion products are discharged into a water bath, which is used asthe heat transfer media for vaporizing the LNG in the tube coil.

In a single burner SCV, combustion air is generally introduced into theburner at two locations. Most of the air enters an upper volute section(secondary combustion air), with the remainder (primary combustion air)being supplied to the region around the fuel gas injector. With thisarrangement, the burner fires upwardly into the central section betweenthe two volutes, where the combustion gases are co-reacted with thesecondary combustion air. The secondary combustion air enters the uppervolute via a tangential inlet, imparting a swirling motion to the air.This results in intimate mixing with the combustion gases rising fromthe burner and subsequent gas recirculation back along the axis of theburner before discharging into a set of sparger tubes located under theprocess tube bundle.

Single point water injection has been discovered herein to reduce NOxemissions. By mounting a water spray at the tip of the burner nozzle,the flame temperature can be lowered, thus retarding thermal NOx. NOxlevels can thus be lowered by at least 50%.

According to preferred aspects of the present invention, the SCV employsa gas nozzle design with water injection that controls the single burnerat maximum operating conditions to produce NOx emissions, corrected to3% dry oxygen (0₂), as low as 30 parts per million (ppm) or less. Thewater injection can be performed using a water spray nozzle cone having,for example, a vertical 60 degree to 90 degree solid cone angle.

A hollow cone, such as a 210 degree hollow cone, is used to direct wateras it is injected into the system. The hollow cone nozzle providesimproved results as compared to a solid cone. It is believed that theimproved performance results from the fact that the water spray isintroduced to combustion air at a different location, thus cooling theflame. Accordingly, NOx emissions from the burner can be reduced to 20ppm or lower.

Referring generally to the figures, this invention provides a burnerassembly such as assembly 10 configured for combusting fuel in acombustion zone to reduce NOx emissions. The burner assembly 10 includesan air nozzle subassembly including an air nozzle conduit 24, such asthat provided by a main burner air nozzle and cooling coil, extendingalong an axis toward the distal end portion of the burner assembly 10.The air nozzle conduit has an interior region to accommodate air flow56.

The burner assembly 10 also includes a gas nozzle subassembly such asgas nozzle assembly 28 including a fuel gas conduit 34 (e.g., includinga fuel gas pipe) positioned at least partially within the interiorregion of the air nozzle conduit. The fuel gas conduit is configured todirect fuel in a direction generally along the axis for delivery to ortoward the combustion zone. The burner assembly 10 further includes anannular passage defined between the air nozzle conduit and the fuel gasconduit (e.g., an annular passage between the main burner air nozzle andcooling coil 24 and the fuel gas pipe 34). The annular passage isconfigured to direct air in a direction generally along the axis fordelivery to or toward the combustion zone.

A water spray subassembly is provided including a water outletconfigured to direct water at an angle with respect to the axis. Thewater outlet is further configured to direct water in a direction towardthe annular passage for mixing with air upstream of the combustion zone.Water is used by way of example only, as other coolant compositionswhich may or may not include water may be used.

The water outlet of the water spray subassembly optionally includes awater spray nozzle such as nozzle 26 or 90. The water spray nozzle canbe configured to direct water in a direction radially outwardly withrespect to the axis. Specifically, the water spray nozzle, such asnozzle 90, may be configured to direct water at a spray angle A3 greaterthan 180 degrees such that an angle A4 between the axis and a spraydirection of the water is less than 90 degrees, or at a spray angle A3from 190 to 230 degrees such that an angle A4 between the axis and aspray direction of the water is less than 85 degrees, or at a sprayangle A3 of about 210 degrees such that an angle A4 between the axis anda spray direction of the water is about 75 degrees.

The water spray nozzle can therefore be configured to direct water in ahollow cone such that water is not directed outwardly from the waterspray nozzle along the axis A. The water spray subassembly optionallyincludes a water conduit such as water pipe 44 positioned to extendwithin the fuel gas conduit, the water spray nozzle being coupled to adistal end of the water conduit. The burner assembly optionally includesan inner annular passage defined between the water conduit and the fuelgas conduit, the inner annular passage being configured to direct fuelin a direction generally along the axis for delivery to the combustionzone. The air nozzle conduit of the air nozzle subassembly may includecooling coils through which water can be circulated.

This invention also provides a method for retrofitting an existingburner assembly for combusting fuel in a combustion zone with reducedNOx emissions. The method can be used with a burner assembly having anair nozzle subassembly including an air nozzle conduit, such as the mainburner air nozzle and cooling coil 24; a gas nozzle subassemblyincluding a fuel gas conduit, such as the fuel gas pipe 34; and a waterspray subassembly including a water outlet, such as nozzle 26 or 90. Themethod includes configuring the water outlet to direct water at an anglewith respect to an axis of the air nozzle conduit and in a directiontoward an annular passage between the air nozzle conduit and the fuelgas conduit for mixing with air upstream of the combustion zone.

The method optionally includes configuring a water spray nozzle, such asnozzle 26 or 90, of the water spray subassembly to direct water in adirection radially outwardly with respect to the axis. Specifically, itincludes configuring the water spray nozzle to direct water at a sprayangle A3 greater than 180 degrees such that an angle A4 between the axisand a spray direction of the water is less than 90 degrees, or at aspray angle A3 from 190 to 230 degrees such that an angle A4 between theaxis and a spray direction of the water is less than 85 degrees, or at aspray angle A3 of about 210 degrees such that an angle A4 between theaxis and a spray direction of the water is about 75 degrees.

The method optionally includes configuring the water spray nozzle todirect water in a hollow cone such that water is not directed outwardlyfrom the water spray nozzle along the axis A.

This invention also provides a method for using a burner system forcombusting fuel in a combustion zone with reduced NOx emissions. Themethod includes directing fuel in a direction generally along an axisfor delivery to the combustion zone through a fuel gas conduit;directing air toward the combustion zone in a direction generally alongthe axis through an annular passage defined between an air nozzleconduit and the fuel gas conduit; and directing water at an angle withrespect to the axis and in a direction toward the annular passage formixing with air upstream of the combustion zone.

The directing water step of the method optionally includes directingwater in a direction radially outwardly with respect to the axis. Forexample, it includes directing water at a spray angle A3 greater than180 degrees such that an angle A4 between the axis and a spray directionof the water is less than 90 degrees, or at a spray angle A3 from 190 to230 degrees such that an angle A4 between the axis and a spray directionof the water is less than 85 degrees, or at a spray angle A3 of about210 degrees such that an angle A4 between the axis and a spray directionof the water is about 75 degrees. The directing water step may alsoinclude directing water in a hollow cone from a water spray nozzle suchthat water is not directed outwardly from the water spray nozzle alongthe axis.

Referring specifically to FIG. 1A, a burner assembly 10 according to oneembodiment of this invention includes a top volute 12 and a bottomvolute 14 for the circulation of air. A cone assembly 16 having a waterjacket extends between the bottom volute 14 and the top volute 12, thusproviding a passage for the flow of combustion products. A partial decksupport 18 is associated with the top volute 12. A burner top plate 20encloses the top volute 12.

Burner assembly 10 is provided with a main burner 22 incorporating awater supply and a spray nozzle, which will be described in furtherdetail later. FIG. 1B shows a cross-sectional view of a distal endportion of the main burner 22. It includes a spray nozzle 26 as will bedescribed in detail below.

Referring now to FIG. 2, components of the assembly of the main burner22 are illustrated in a cross-sectional elevation view. Main burner 22generally includes an air nozzle subassembly, a gas nozzle subassembly,and a water spray subassembly. Specifically, main burner 22 includes amain burner air nozzle and cooling coil 24. The main burner air nozzleand cooling coil 24 is coupled to receive a supply of air that generallyflows upwardly through the main burner air nozzle and cooling coil 24.

Main burner 22 also includes a gas nozzle assembly 28 and a water nozzleassembly 30 that is positioned at least partially within the gas nozzleassembly 28. The gas nozzle assembly 28 is attached via a coupling 32 toa fuel gas pipe 34. In turn, fuel gas pipe 34 is coupled via a tee 36 toa fuel gas pipe 38. The fuel gas pipe 38 is in turn coupled via an elbow40 to provide a fuel gas inlet 42. The inlet 42 is connected to a sourceof fuel gas (not shown).

The water nozzle assembly 30 is coupled to a source of water via a waterpipe 44. The water pipe 44 is coupled via an elbow 46 to a water pipe48, which is in turn coupled via an elbow 50 to provide a water inlet52. The inlet 52 is connected to a source of water or other coolant (notshown).

As is generally indicated by the arrows in FIG. 2, a passageway isdefined for fuel gas flow 54 in a general direction toward the distalend portion of the main burner 22. Concurrently, a passage is definedfor water flow 58 toward the distal end portion of the main burner 22such that the water flow 58 generally flows in a passage or conduitdisposed within the fuel gas flow 54. A passageway is defined betweenthe cooling coil 24 and the fuel gas pipe 34 for air flow 56, also inthe general direction toward the distal end portion 23 of the mainburner 22.

As will be understood, main burner 22 is configured for combustion ofthe mixture of fuel and air including the fuel of fuel gas flow 54, theair of air flow 56, and air in the base of volute 14. This combustiongenerates a flame shown generally at 25 in FIG. 2, extending in adirection along the axis of the main burner 22, which is oriented alonga vertical axis A in the embodiment illustrated in FIG. 2. The base ofthe flame will generally be positioned a short distance beyond thedistal end of the main burner 22 along axis A. Referring back to FIG.1A, the flame will extend toward or into the cone assembly 16.

Referring to FIGS. 3A and 3B, the distal end portion of main burner 22is illustrated in top and side views, respectively. The main burner 22includes the water spray nozzle 26 that extends above a top plate 62 ofthe main burner 22. A pair of lugs 64, offset by 180° in thisembodiment, extend radially outward from the axis A of the main burner22 for purposes of providing anchorage for an installation tool. Mainburner 22 also includes a pipe 66 having a wall with a plurality ofports 68 or holes formed therein through which fuel gas flow 54 fromwithin the pipe 66 can be directed.

Referring now to FIG. 4, the distal end portion of the main burner 22 isshown in a cross-sectional view in order to illustrate the generaldirections of fuel gas flow 54 and water flow 58. These flows aredirected generally in the same direction along the axis of the mainburner 22 (e.g., in a direction parallel or approximately parallel tothe axis A). The water flow 58 moves through the water pipe 44 of thewater spray subassembly. The fuel gas flow 54 moves in the annularpassage defined between the inner surface of the fuel gas pipe 34 andthe outer surface of the water pipe 44.

Referring now to FIGS. 4, 5A and 5B, features of the water spraysubassembly are illustrated in side elevation and top views,respectively. The water spray subassembly includes a water pipe portion70 of water pipe 44 extending from a pipe coupling 72. Upper centeringmembers 74 (three being illustrated by way of example only as spokes inthis embodiment) extend radiantly outward from the water pipe portion 70and is generally located a distance D from the distal end of the pipecoupling 72. The upper centering plate 74 has a thickness T and isconfigured to provide a centering function such that water pipe portion70 of water pipe 44 can be centered within the fuel gas pipe 34 of themain burner 22. A lower centering plate 76 is also provided for thispurpose.

The components of the water spray subassembly are shown in FIG. 5A. Ithas a length L selected depending upon the size of the main burner 22.As is illustrated in FIG. 5B, the upper centering spokes 74 extendoutwardly to a distance similar to a diameter of the lower centeringplate 76, and such spokes are spaced from one another at an angle A1(e.g., 120°).

Referring now to FIG. 6, details of the distal end portion of the mainburner 22 are illustrated according to one exemplary embodiment. Thewater spray nozzle 26 in this embodiment is a solid cone spray nozzlehaving a water spray cone angle A2. Accordingly, water flow 58 movesthrough the water pipe portion 70, through the coupling 72, and througha nozzle opening of water spray nozzle 26 to be directed upwardly fromthe distal end of the main burner 22 in a solid cone. The water spraycone angle A2 is the included angle of the solid spray cone generated bythe water spray nozzle 26.

The main burner 22 also includes, at its distal end portion, a mountingring 78, which provides a support for one or more gaskets 80 or seals.The mounting ring 78 and gaskets 80 provide a means for sealing againstthe plate 62 of the main burner 22, thereby reducing or preventing theflow of fuel gas through the space between the coupling 72 and anaperture 73 in the end plate 62. The seal is shown in FIG. 6 in brokenlines, such that the position of the mounting ring 78 and gasket 80would be adjusted such that the gasket 80 contacts a bottom surface 63of the end plate 62, thereby providing the seal. This position of thegasket 80 is shown in broken lines in FIG. 6. Thus, substantially all ofthe fuel gas flow 54 is discharged through the gas nozzle assembly 28through the ports 68 in the pipe forming the gas nozzle assembly 28.

FIG. 7 shows another exemplary embodiment of this invention illustratedin a cross-sectional, enlarged view of the distal end portion of a mainburner 22. Elements illustrated in FIG. 7 which correspond to theelements described above with respect to FIGS. 1A-6 have been designatedby corresponding reference numbers increased by one hundred. The nozzle90 structure illustrated in FIG. 7 differs somewhat from the nozzle 26illustrated in FIG. 6. For example, the water spray nozzle 90 provides ahollow cone spray instead of a solid cone water spray.

More specifically, the nozzle 90 redirects water flow 158 so that itwill be discharged in a hollow cone radially outward from the axis A ofthe main burner. In this way, the water is redirected radially outwardand away from the base of the flame that will form at a location beyondthe distal end of the main burner along axis A. By using a hollow conespray shape at the distal end of the burner, it is possible to redirectwater flow in a spray shape away from the flame. Also, such a sprayshape makes it possible to redirect the water spray toward or into thepath of air flow upstream of the combustion zone. Although variousnozzle configurations may be used, one suitable nozzle embodiment is ahollow cone spray nozzle such as a Type PJ nozzle available from DelavanSpray Technologies of Delavan Ltd, which is a wholly owned subsidiary ofGoodrich Corporation. Such a nozzle is designed to produce a hollow conespray pattern using an external ‘pintle’ deflector.

The water spray nozzle 90 is configured to form a water spray hollowcone angle A3 as illustrated in FIG. 7. Although a wide variety of waterspray cone angles A3 may be selected, a spray angle A3 greater than 180°is used for reasons explained later. When the water spray angle A3 isgreater than 180°, the angle A4 between the axis of the main burner anda spray direction of the water is less than 90°. The spray angle A3 isin a range from 190° to 230° such that an angle A4 between the axis andthe spray direction of the water is from 65 to 85°. For example, in oneembodiment the spray angle A3 is about 210° such that an angle A4between the axis and the spray direction of the water is about 75°.

The water is introduced into the angular passage 29 that extends betweenthe inner surface of main burner air nozzle and cooling coil 24 and theouter surface of the fuel gas pipe 34 or the outer surface of the gasnozzle assembly 28. In other words, water is directed into the air flow56 as it passes through the main burner air nozzle and cooling coil 24.

This direction of the water spray entrains the water into the air flow56 prior to and upstream of the combustion zone, thus further reducingNOx emissions generated by the flame of the burner. Additionally, thewater spray encourages mixing with air upstream of the combustion zonerather than directing water along the axis A into the base of the flame.

Although the water is introduced into the air using a water spray nozzleat the distal end portion of the burner assembly in the illustratedembodiments, it is contemplated that the water could be introduced atany location in the air upstream from the location of the flame,preferably within the passageway through which air flow 56 is introducedinto the area of combustion. For example, water can be introduced at anylocation along the path of water flow 58, including at the base in thearea of the elbow 46 or anywhere else along the path of water flow 58.

Alternatively, water flow can be introduced into the air flow 56radially inwardly from the structure of the main burner air nozzle andcooling coil 24. For example, water can be introduced from the coolingcoil into the air flow 56 by placing one or more nozzles in the coolingcoil facing radially inward toward the fuel gas pipe 34 or gas nozzleassembly 28. In other words, a portion of the water flowing through thecooling coil can be utilized for the reduction of NOx emissions bydirecting it radially inward to be entrained within the air flow 56upstream of the combustion zone.

EXAMPLES

Data was taken for NOx reduction in a water injection nozzle test. Stackemissions data points were recorded on an LNG vaporizer. Readings weretaken with a system incorporating the water injection nozzle shown inFIG. 6 (˜92° solid cone spray pattern A2). Test readings were also takenwith the water injection nozzle shown in FIG. 7 (210° hollow cone spraypattern A3).

The test readings are reported in the following table:

LNG Flow Nozzle Type (MMSCFD) CO Reading NOx Reading solid cone spray100 2.8 PPM 30.4 PPM pattern solid cone spray 145 4.0 PPM 23.5 PPMpattern solid cone spray 190 2.9 PPM 25.8 PPM pattern hollow cone spray100 1.3 PPM 24.4 PPM pattern hollow cone spray 145 2.3 PPM 17.7 PPMpattern hollow cone spray 190 1.2 PPM 21.1 PPM pattern Abbreviationsused: MMSCFD—Million Standard Cubic Feet per Day CO—Carbon MonoxideNOx—Generic term for the mono-nitrogen oxides NO and NO₂ (nitric oxideand nitrogen dioxide) PPM—Parts per Million

The foregoing test illustrates that a further reduction of NOx occurswhen the water spray nozzle 26 of FIG. 6 is replaced with the waterspray nozzle 90 with a hollow cone spray instead of a solid cone waterspray. More specifically, water spray nozzle 90 redirects water flow 158so that it will extend in a hollow cone radially outwardly from the axisA of the main burner. In this way, the water is redirected radiallyoutward and away from the base of the flame that will form at a locationbeyond the distal end of the main burner along axis A. This facilitatesentrainment of water into the air upstream of the point where the airenters the combustion zone, thus reducing NOx emissions.

While embodiments of the invention have been shown and described herein,it will be understood that such embodiments are provided by way ofexample only. Numerous variations, changes and substitutions will occurto those skilled in the art without departing from the spirit and scopeof the invention. Accordingly, it is intended that the disclosure hereincovers all such variations and modifications as fall within the spiritand scope of the invention.

1. A burner assembly for combusting fuel in a combustion zone to reduceNOx emissions, comprising: an air nozzle subassembly including an airnozzle conduit extending along an axis toward a distal end portion ofthe burner assembly, the air nozzle conduit having an interior region toaccommodate air flow; a gas nozzle subassembly including a fuel gasconduit positioned at least partially within the interior region of theair nozzle conduit, the fuel gas conduit configured to direct fuel in adirection generally along the axis for delivery to the combustion zone;a passage arranged between the air nozzle conduit and the fuel gasconduit, the passage configured to direct air in a direction generallyalong the axis for delivery to the combustion zone; and a water spraysubassembly including a water outlet configured to direct water at anangle with respect to the axis, the water outlet further configured todirect the water in a direction toward the passage for mixing with theair upstream of the combustion zone.
 2. The burner assembly of claim 1,wherein the water outlet comprises a spray nozzle.
 3. The burnerassembly of claim 2, wherein the spray nozzle is configured to directthe water in a direction radially outward with respect to the axis. 4.The burner assembly of claim 3, wherein the spray nozzle is configuredto direct the water radially outward at a spray angle greater than 180degrees such that an angle between the axis and a spray direction of thewater is less than 90 degrees.
 5. The burner assembly of claim 4,wherein the spray nozzle is configured to direct the water radiallyoutward at a spray angle from 190 to 230 degrees such that an anglebetween the axis and a spray direction of the water is less than 85degrees.
 6. The burner assembly of claim 5, wherein the spray nozzle isconfigured to direct the water radially outward at a spray angle ofabout 210 degrees such that an angle between the axis and a spraydirection of the water is about 75 degrees.
 7. The burner assembly ofclaim 3, wherein the spray nozzle is configured to direct water radiallyoutward in a hollow cone such that the water is not directed outwardfrom the spray nozzle along the axis.
 8. The burner assembly of claim 3,wherein the water spray subassembly further comprises a water conduitextending within the fuel gas conduit, and the spray nozzle is connectedto a distal end of the water conduit.
 9. The burner assembly of claim 8,further comprising an inner annular passage disposed between the waterconduit and the fuel gas conduit, the inner annular passage configuredto direct the fuel in a direction generally along the axis for deliveryto the combustion zone.
 10. The burner assembly of claim 1, wherein theair nozzle conduit comprises cooling coils through which the water canbe circulated.
 11. A method for combusting fuel in a combustion zone toreduce NOx emissions, comprising: providing fuel through a fuel gasconduit in a direction generally along an axis for delivery to thecombustion zone; providing air toward the combustion zone in a directiongenerally along the axis through an annular passage disposed between anair nozzle conduit and the fuel gas conduit; and providing water at anangle with respect to the axis and in a direction toward the annularpassage for mixing with air upstream of the combustion zone.
 12. Themethod of claim 11, wherein the providing water comprises directing thewater in a direction radially outward with respect to the axis.
 13. Themethod of claim 12, wherein the providing water comprises directing thewater radially outward at a spray angle greater than 180 degrees suchthat an angle between the axis and a spray direction of the water isless than 90 degrees.
 14. The method of claim 13, wherein the providingwater comprises directing the water radially outward at a spray anglefrom 190 to 230 degrees such that an angle between the axis and a spraydirection of the water is less than 85 degrees.
 15. The method of claim14, wherein the providing water comprises directing the water radiallyoutward at a spray angle of about 210 degrees such that an angle betweenthe axis and a spray direction of the water is about 75 degrees.
 16. Themethod of claim 11, wherein the providing water comprises directingwater radially outward in a hollow cone from a water spray nozzle suchthat the water is not directed outward from the water spray nozzle alongthe axis.